The present invention relates to a backfire-resistant gas-torch construction, as for applying metallic coating material to a substrate. The invention has application to gas-torch configurations other than for flame deposition of metal coatings; for example, the invention is applicable to such gas-torch employments as welding, surface-melting, cutting, flaming, and flame-depositions other than of metal. However, the presently disclosed embodiments have metal-coating capability. The term "backfire-resistance" as presently used shall imply that gas-mixture explosions within the torch or applicator are avoided.
Applicators of the backfire-resistant type have recently become known and have been used especially for powder flame spraying, with the backfire resistance being safeguarded by special nozzle formations. Previous systems, with nozzles, had been supplied with combustible-gas components which were mixed and therefore ignitable and explosive at a location upstream from the nozzle. In a more recent construction, mixing is no longer effected at a suitable point within the device but rather within the nozzle itself, the mixing being substantially only immediately prior to discharge from the nozzle.
"Internally mixing" nozzles have been known per se from cutting torches in which the backfire-resistance requirement is not as important as with devices for applying metallic coatings. The internally mixing cutting-torch nozzles have involved different approaches to a solution, but these approaches have not been entirely satisfactory.
Although highly desirable, the provision of conventional torch systems with backfire-resistant, internally mixing nozzles has not been possible, without development of a special device uniquely designed to serve the particular nozzle. And it should be noted that, in contrast to simple welding and cutting torches, the provision of powder flame-spraying capability presents special problems of accommodating the mixing and supply of powder with carrier gas, the sealing of metal connecting faces, etc. within a minimum of available spaces. These problems are aggravated by the fact that component-gas supply-line terminations at the torch body generally do not register with corresponding connection openings of the internally mixing nozzle; for example, a connection of the nozzle to the torch body (which is, as a rule, of gun or pistol-shaped configuration) is prevented, due to mismatch or non-symmetry of connection relationships.
In the indicated recently known system, this connection problem has not been solved optimally, in that a fixed stationary block has been incorporated into the system, with small individual tubes provided for conduct of the gas-component flows to the nozzle-connecting face. To assure a proper operation of the device, the nozzle must be clamped firmly and closely against the metal connecting face of the block. Such clamping usually requires use of a vise or the like, thus presenting a particular disadvantage in coating operations, where nozzle replacement is frequently required, it being noted that the vise or the like is also needed to unscrew the nozzle clamp for nozzle replacement.
Apart from the fact that it is thus necessary to clamp the whole of the system in a complicated manner, it is not only possible for the housing to become externally damaged, but damage can also occur to the metallic sealing face, e.g., by unnoticed small powder particles that may remain as a result of repeated assembly and disassembly of the nozzle. Moreover, the multiple passages required by existing mixing-nozzle devices present unusual problems of sealing all connections, making it unavoidable to use thermally loadable soft-ring seals. And the heat developed at the nozzle can dissipate only via the torch body, causing excessive heat at the connection area for the powder-storing vessel.